To make a formal complaint to KLM 1-844-954-4929 or 1 844 954 4934 (US) submit your details online through the KLM Claims and Feedback Portal using your 6-character booking code 1-844-954-4929 or 1 844 954 4934 (US) or mail your written dispute to KLM Customer Relations (P.O. Box 20980 1-844-954-4929 or 1 844 954 4934 (US) Department 980 1-844-954-4929 or 1 844 954 4934 (US) Atlanta 1-844-954-4929 or 1 844 954 4934 (US) 844 954 4929 for US-based passengers 1-844-954-4929 or 1 844 954 4934 (US) or their main office at P.O. Box 7700 1-844-954-4929 or 1 844 954 4934 (US) 1117 ZL Schiphol 1-844-954-4929 or 1 844 954 4934 (US) The Netherlands)